1. Field of the Invention
The present invention relates to a resist lower layer composition, a resist lower layer film-formed substrate and a patterning process used for formation of a layer lower than a resist upper layer film, which is useful for a multi-layer resist method favorably used in microfabrication in manufacturing of a semiconductor device and the like.
2. Description of be Related Art
As LSI is progressing toward a higher integration and a faster speed in recent years, further miniaturization of a pattern rule is required. Under such a movement, a lithography using a light exposure, which is a widely used technology today, is reaching a limit of its resolution power inherent to a wavelength of a light source.
As a light source for a lithography used in a resist patterning process, light-exposures with a g-line (436 nm) or an i-line (365 nm) of a mercury lamp have been widely used. For further miniaturization, a method in which an exposing light is shifting toward a shorter wavelength has been considered to be effective. Accordingly, in place of an i-line (365 nm), a KrF excimer laser (248 nm), which emits a shorter wavelength than the i-line, has been used in a mass production process for a 64 Mbit DRAM. However, for production of DRAM with an integration of 1 G or more, which requires a further miniaturized process technology (processing dimension of 0.13 μm or less), a light source with a further shorter wavelength is required, and thus, a lithography using an ArF excimer laser (193 nm) has been investigated particularly.
On the other hand, it has been known in the past that a multi-layer resist process such as a two-layer resist method is excellent in formation of a pattern having a high aspect ratio on a nonplanar substrate. As for a two-layer resist method, to develop a two-layer resist film by a generally used alkaline developer, a silicone polymer having a hydrophilic group such as a hydroxy group and a carboxyl group is preferable.
As such a silicone polymer, a silicone-type positive resist composition of chemically amplified type using a base resin, which is obtained by protecting a part of a phenolic hydroxy group of polyhydroxybenzyl silsesquioxane, a stable alkaline-soluble silicone polymer, with a t-Boc group, together with an acid generator is proposed for a KrF excimer laser (see, for examples, Japanese Patent Laid-Open (kokai) No. H6-118651 and SPIE Vol. 1925 (1993), p. 377). For an ArF eximer laser, a positive resist composition based on a silsesquioxane whose cyclohexyl carboxylic acid is substituted with an acid-labile group is proposed (see, for example Japanese Patent Laid-Open (kokai) No. H10-324748, Japanese Patent Laid-Open (kokai) No. H11-302382, and SPIE Vol. 3333 (1998), p. 62). Further, a positive resist composition based on a silsesquioxane having a hexafluoroisopropanol as a soluble group is proposed for an F2 excimer laser (see, for example, Japanese Patent Laid-Open (kokai) No. 2002-55456). The above-mentioned polymers contain a polysilsesquioxane having a ladder skeleton in their main chain made by polycondensation of a trialkoxy silane or a trihalogenated silane.
As a silicone polymer having a silicon pendant on its side chain, a polymer of a silicon-containing (meth)acrylate ester is proposed (see, for example Japanese Patent Laid-Open (kokai) No. H9-110938 and
J. Photopolymer Sci. and Technol., Vol. 9, No. 3 (1996), p. 435-446).
A resist lower layer film in a two-layer resist method is formed of a hydrocarbon compound, which can be etched by an oxygen gas, and in addition, which is desired to have a high etching resistance because it becomes a mask when a substrate under it is etched. For etching by an oxygen gas when etching of the resist lower layer film using a resist upper layer film as a mask, the resist lower layer film is desired to be composed of only a hydrocarbon, not containing a silicon atom. In addition, the resist lower layer film desires to have a function as an anti-reflection film in order to improve a controllability of a line width of a silicon-containing resist upper layer film and to form less bumps on a pattern sidewall and to reduce collapsing of a pattern by a standing wave. Specifically, a reflectance from a resist lower layer film to a resist upper layer film is desired to be made 1% or less.
Meanwhile, a three-layer resist method has been proposed which is configured to stack: a single-layer resist without containing silicon, as a resist upper layer film; a resist intermediate-layered film containing silicon, thereunder; and a resist lower layer film comprising an organic film, thereunder (see J. Vac. Sci. Technol., 16(6), November/December 1979, for example). Generally, single-layer resists are more excellent in resolution than silicon-containing resists, and it is possible to adopt a single-layer resist exhibiting a higher resolution as an exposure imaging layer in the three-layer resist method. As the resist intermediate-layered film, a spin-on-glass (SOG) film is used, and many SOG films have been proposed.
Here, the optimum optical constants of a resist lower layer film for restricting a substrate reflection in the three-layer resist method are different from those in the two-layer resist method.
Although the two-layer resist method and the three-layer resist method are the same in terms of the purpose to restrict the substrate reflection as less as possible, concretely, down to 1% or less, the three-layer resist method is allowed to cause one or both of a resist intermediate-layered film and a resist lower layer film to possess an antireflective effect whereas the two-layer resist method is configured to cause only a resist lower layer film to possess an antireflective effect.
Incidentally, silicon-containing layer compositions configured to possess antireflective effects have been proposed in U.S. Pat. No. 6,506,497 and U.S. Pat. No. 6,420,088 and the like, for example.
Further, it is also known that a multi-layered antireflective film has a higher antireflective effect than a single-layered antireflective film, and multi-layered antireflective films are being widely and industrially used as antireflective films of optical parts, eyeglasses, and the like. Namely, it is possible to obtain a higher antireflective effect by causing both a silicon-containing resist intermediate-layered film and a resist lower layer film to possess antireflective effects.
Moreover, the resist lower layer film in case of the three-layer resist method is required to possess a higher etching resistance during substrate processing, in addition to the effect as an antireflective film.
Thus, as a resist lower layer film for the three-layer resist method, it is preferable to use a polymer having a higher etching resistance, containing more aromatic groups, and having a higher ratio of carbon atoms.
Under such circumstances, low-dielectric insulator films have been recently and increasingly used as layers to be processed of substrates. As low-dielectric insulator films for achieving specific dielectric constants of 2.5 or less, porous silicas having specific dielectric constants of 1 and having vacancies have been investigated.
However, one of problems in the case of adopting low-dielectric insulator films based on porous silica, is footing (poisoning) of a positive resist after development. As a reason thereof, it has been considered that amine substances are adsorbed to vacancy portions, and the amine substances are released from the vacancy portions and passed through a resist lower layer film to cause a neutralizing reaction with acid in an overlying resist film to cause the footing, during a resist patterning process, particularly during baking (see J. Photopolymer Sci. and Technol. Vol. 16 No. 3 (2003) p351-361). It is therefore desired to elaborate a resist lower layer film capable of mitigating adverse effects such as footing in an overlying resist film to be caused by amine substances.
As methods for prevention of poisoning, there have been proposed a lower layer film configured to generate a sulfonic acid residue such as by heating (Japanese Patent Laid-Open (kokai) No. 2004-177666, and Japanese Patent Laid-Open (kokai) No. 2004-179393, for example), and a lower layer film additively including an amine salt of a polymeric fluorosulfonic acid (Japanese patent application No. 2005-120636, for example). Although lower layer films each additively including a polymer having an acidic group are free of concern of evaporation of the acid due to baking, the acidic group is fixed, thereby exhibiting such a disadvantage of a decreased ability to neutralize a basic substance which is produced from a substrate as a cause of poisoning.
Methods have been conventionally known to improve resist pattern profile in a manner to add an acid or an acid generator into a layer lower than a resist upper layer film, and there have been exemplarily proposed: an intermediate-layered film adapted to a three-layer resist method and comprising a silicone resin additively including an ammonium salt for generating an antimonate (Japanese Patent Laid-Open (kokai) No. H5-267158, for example); an intermediate-layered film for a three-layer resist method and additively including an acid generator (Japanese Patent Laid-Open (kokai) No. H5-291130, for example); and the like.
However, although the added type of acid generator exhibits a higher anti-poisoning ability when the produced acid remains in the film, the acid generator brings about a problem of a lowered anti-poisoning ability due to evaporation of the acid by baking upon cross-linking. In this respect, although a higher anti-poisoning effect can be expected by perfluorosulfonic acid as a super strong acid, this acid has a lower boiling point and thus evaporates upon baking, thereby deteriorating the anti-poisoning effect.
Although alkyl sulfonic acids such as camphorsulfonic acid are high in boiling point, they are weak acids and are thus lower in amine trapping ability. Further, although inorganic acids such as antimonate are strong acids and are high in boiling point, metallic acids are not allowed to be used in a semiconductor application. In turn, an ammonium salt has a thermal decomposition temperature lower than those of onium salts such as iodonium salt and sulfonium salt, and is capable of generating an acid by low-temperature baking to thereby cure an associated film. The lowered baking temperature means that evaporation of an acid is prevented to improve an anti-poisoning effect. Here, there have been disclosed: a lower layer film including an acid generator of an ammonium salt type of toluenesulfonic acid (Japanese Patent Laid-Open (kokai) No. 2003-114533 and Japanese Patent Laid-Open (kokai) No. 2005-331951, for example); exemplification of nonafluorobutanesulfonate triethylamine salt in the body text (Japanese patent application No. 2002-372829, for example); and example of nonafluorobutanesulfonate tripropylamine salt (Japanese patent application No. 2004-28506, for example).
In such multi-layer resist methods, acid crosslinking agents, thermal acid generators and the like in resist lower-layer compositions have increasingly come to exhibit important roles. For promotion of a cross-linking reaction by heating, there is required a thermal acid generator for generating a strong acid. Although thermal acid generators for generating perfluoroalkylsulfonic acids have been preferably adopted for that purpose, trifluoromethanesulfonic acid, nonafluorobutanesulfonic acid, and the like having lower molecular weights are problematically high in volatility, thereby bringing about a possibility of volatilization upon cross-linking reaction. Meanwhile, although perfluorooctanesulfonic acid having a long-chain alkyl group is not so problematic in terms of volatility, its biologically concentrating property and accumulative property caused by a stability (indecomposability), hydrophobicity, and lipophilicity derived from C—F bonds have become problematic, thereby internally containing a harmfulness problem and an environmental problem. The Environmental Protection Agency (EPA) in US has covered 13 substances and 75 substances relating to perfluorooctanesulfonic acids: PFOS's in the significant new use rules, respectively. Note that although adoptions of the 75 substances for resist application are exempted from notification, it is desired to elaborate a composition so as to exclude usage of PFOS's in view of the aforementioned harmfulness problem and environmental problem.
To cope with the problem concerning PFOS's, elaborations have been conducted by companies to obtain partially fluorine-substituted alkyl sulfonic acids configured to have decreased fluorine substitution rates, respectively. For example, Japanese translation of PCT international application No. 2004-531749 has elaborated α,α-difluoroalkyl sulfonate from α,α-difluoroalkene and a sulfur compound, and exemplified a resist composition containing a photoacid generator for generating a corresponding sulfonic acid by exposure, concretely, containing (4-tert-butylphenyl)iodonium-1,1-difluoro-1-sulfonate-2-(1-naphthyl)ethylene; and the Japanese Patent Laid-Open (kokai) No. 2004-2252 has elaborated α,α,β,β-tetrafluoroalkyl sulfonate from α,α,β,β-tetrafluoro-α-iodoalkane and a sulfur compound, and exemplified a photoacid generator for generating a corresponding sulfonic acid, and a resist composition. Further, although synthesis examples of actual compounds are not disclosed in the Japanese Patent Laid-Open (kokai) No. 2002-214774, numerous photoacid generators for generating partially fluorinated alkyl sulfonic acids and resist compositions are disclosed therein. However, numerous problems are left, such as difficulties in obtainment of intermediate products of raw materials and in production methods. Moreover, descriptions in the references are related to utilization of such sulfonates as photoacid generators only, and no descriptions are found therein concerning utilization of the sulfonates in resist lower-layer compositions.
In this way, it is desired to elaborate a resist lower-layer composition which exhibits a higher anti-poisoning effect in a multi-layer resist method, and which is low in environment load.